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Abstract

The crystal structures and Hirshfeld surface analyses are reported for four aldoximes, (E)-X–C6H4CH=N–OH [X = 3-Cl (1), 4-F (2), 2-O2N (3) and 4-O2N (4)]. The strong classical O–H · · · N hydrogen bonds involving the oxime group generate C(3) chains in compound 1, in contrast to the R22(6) dimers formed in compounds 2–4;
such arrangements have been shown to be the most frequently found for
oximes other than salicylaldoximes (2-hydroxybenzaldehyde oximes). In
general, weaker intermolecular interactions involving the X
substituents, as well as C–H · · · O and π · · · π interactions have
significant effects on the supramolecular arrays generated in the
aggegation. A further important interaction in compound 1, and to a lesser extent in compound 4,
is a π(C=N) · · · π(phenyl) molecular stacking. A data base search has
indicated that short Cg(C=N) · · · Cg(phenyl) distances, <3.3 Å
(Cg = centre of gravity), have been found in various compounds,
including other oximes. A theoretical study was carried out starting
from the crystal structure data of compound 1, with
optimisation at the BLYP-D3/def2-DZVP level, as well as at the higher
PBE0/ma-def2-TZVP level. Breakdown of the interaction energy into
separate contributions was achieved using SAPT (using the jun-cc-pvdz
basis set). Overall, the calculations indicate that the π(C=N)
·· · π(phenyl) interaction is attractive, with a magnitude of 14–18 kJ
mol−1.